First of all Jitsi isn't part of the rocketchat-server package, so you need to set it up yourself or use a hoster, which both require separate accounts from the RocketChat ones.
The specific issue I had on Windows was that RocketChat wasn't registered to handle jitsi-meet:// links, it would just open a blank "open with" Windows dialog everytime. In general the "integration" seems lacking, the whole UX is really bad compared to Matrix/Element where voice calls just work.